Aircraft include one or more movable flight control members such as ailerons on the wings for roll control, elevators on the horizontal tail of the empennage for pitch control, a rudder on the vertical tail of the empennage for yaw control, a nose cone of a missile, and other movable control surfaces. Movement of a flight control member is typically effected by one or more actuators mechanically coupled between a support member (e.g., a wing spar) and the flight control member. In many aircraft, the actuators for flight control members are linear hydraulic actuators driven by one or more hydraulic systems.
Hydraulic systems for aircraft are designed to provide hydraulic fluid to the hydraulic actuators to move and position the flight control members as necessary during the flight of the aircraft. The hydraulic systems can include a series of supply and return lines. One or more actuators are positioned along the supply and return lines and are attached to the flight control members. One or more pumps move the hydraulic fluid through the hydraulic system and supply it to the actuators. The hydraulic fluid is directed into different sections of the actuator to elongated and shorten the actuator and thus adjust the flight control member. The hydraulic fluid from the actuator is moved into the return line which returns the hydraulic fluid to the pump to be reused in the hydraulic system.
Valves are positioned near the actuators to control the movement of fluid into and out of the actuators. The valves should provide the flow of the hydraulic fluid to control the actuators during varying loads that are placed on the flight control members, and to meet rate demands for movement of the flight control members. The valves should be configured to provide the necessary hydraulic fluid to provide effective movement of the flight control members during a flight.